Problem: What is the greatest common factor of $45$ and $15$ ? Another way to say this is: $\operatorname{gcf}(45, 15) = {?}$
Solution: The greatest common factor is the largest number that is a factor of both $45$ and $15$ The factors of $45$ are $1$ $3$ $5$ $9$ $15$ , and $45$ The factors of $15$ are $1$ $3$ $5$ , and $15$ Thus, the greatest common factor of $45$ and $15$ is $15$. $\operatorname{gcf}(45, 15) = 15$